This invention relates to a compass that can be used in military vehicles to designate true north while the vehicle is changing directions. A special aim is to provide a compass that is unaffected by large iron masses in the hulls or turrets of military vehicles.
I have designed the compass to include a platform that rotates in a horizontal plane at a relatively high rotational speed, e.g. 100 revolutions per minute. A frame structure is swingably mounted on the platform for upward angulation to a setting that will establish a north star sight line when the platform is at some point in its cycle of revolution. An elongated columnar element is oriented on the north star sight line for slow rotational motion at a speed of one twenty fourth revolution per hour, i.e. one complete revolution per day. The columnar element provides a support surface for a telescope that is designed to intermittently sight the sun while the sun is passing overhead during the course of each day. Periodically adjustments are made in the angle between the columnar element and telescope sight line, whereby the telescope is ensured of sighting the sun during all seasons, e.g. summer, winter, etc.
When the instrument is in use two motions take place. The platform rotates at a high speed in a horizontal plane; for an instant during each revolution of the platform the columnar element is aligned with the north star. The slow rotation of the columnar element enables the telescope to have a potential sight line on the sun at one point during each revolution of the platform. If the columnar element and telescope are properly adjusted the telescope will sight the sun at the precise instant when the columnar element is aligned with the north star. A flicker of light in the telescope will indirectly indicate a north-seeking orientation of the columnar element.
The compass contains a circular array of fibre optic bundles optically connected to the telescope. A flickering light output at any one of the fibre optic bundles will indicate a north-seeking attitude of the columnar element. Frequency of the light output is the same as the rotational speed of the platform, e.g. 100 cycles per minute, sufficient for human viewing purposes. The platform rotational speed is not critical; higher or lower speeds can be used.
The rotating platform is an important feature of the invention since it enables the compass to operate whatever the direction being taken by the moving vehicle. The rapidly rotating platform causes the columnar element to have a north star-seeking orientation at some point during each revolution of the platform irrespective of which direction the vehicle might then be taking. The instant at which the columnar element is in the north-seeking orientation is not precisely known. However that is not of any great importance since the rapidly rotating platform enables the columnar element to achieve the desired orientation at a high frequency, e.g. 100 time per minute in the example system.
My invention is particularly intended for use in military vehicles where the large iron mass would adversely affect the performance of magnetic compass systems. I believe that my compass will be cheaper to build than gyroscopic compass systems.